Transmission of pictures by electricity



Aug. 18, 1925. 1,550,570

M. B. LONG TRANSMISSION OF PICTURES BY ELECTRICITY Filed Aug. 14, 1924 Redified Current Min-l7 W iUiJi Patented Aug. 18, 1925.

'um'rso STATES PATENT OFFICE.

MAUBI'JE B. LONG, OFVGL EN RIDGE, NEW JERSEY, ASSIGNOB T6 WESTERN'ELEGTBIC GOMIANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OI NEW YORK.

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. Application filed au ust 14,1924. Serial no. 731,946.

T0 all whom it may co'ncem:

Be it known that I, MAURICE B. LoNo, a citizen of the United. States, residing at Glen Ridge, of New Jersey, have invented certain new and useful Improvements in Transmission of Pictures by lectricity, of which the following is a full, clear, concise, and exact description.

This invention relates to a the transmission of pictures by electricity and more particularly to reproducing equipment for such a-system.

It was known prior to this invention that pictures could be transmitted from one place to another by means of electric currents, some characteristic of which was varied in accordance with the tone values of succes sive elemental areas of the picture. In a common form of equipment, the amplitude of the current is varied at the sending terminal, which varying current is employed at the reproducing terminal to actuate the reproducing equipment.

An object of the present'invention is to increase the flexibility of the reproducing equipment. I

Another object is to effect the reproduction as either a positive or negative of the original picture, independently of the sending terminal.

In one embodiment of the invention, the tone values of the elemental areas of the picture to be transmitted are sent as modulations of a voice frequency carrier wave. At the reproducing terminal, this wave is demodulated in a three-electrode electron discharge device, the demodulated current being used to operate an electromagnetic light valve. for controlling the ex osure of in the county of Essex, State system for The invention, both "other objects and advantages thereof, will be further explained in the following. description. having panying drawing. 4

Flg. l of the drawing is a schematic diagram of a system in which an electron discharge device functions as the demodulator.

Fig. 2 isa diagramv which will be used in explanation of the operationof the system of Fig. 1.

reference to the adcomas its organization l and method of operation together with Fig. 3 is a schematic diagram of the red producing equipment wherein the light valve functions as the demodulator.

Figs. 4 and 5 show the relative positions of the light valve strings for dilferent conditions, the elements being greatly enlarged.

Referring now to Fig, l rotatable drums 5 and 6 are mounted on shafts 7 and 8 which are caused to rotate in any suitable manner. As the drums rotate, they are caused tomove axially with respect to the shafts. Upon the drum 5, there is mounted a transparency 9 of the picture which is to be transmitted.

Mounted upon the drum 6 is a record blank 10, such as a sensitive photographic paper or film. Located within the drum 5 and transparency 9 is a photo-electric cell 11, the

electrical characteristic of which is affected .by the amount of light received from a source 12, through a lens 13 which projects an image of the light source 12 upon the transparency 9 of the picture. The amount of light reaching the photo-electric cell 11 is determined by the tone value of the elemental area of the transparency 9 which is opposite the focal point of lens 13 at any given time.

The terminals of the photo-electric cell 11, are connected to a modulating device 14, whereby carrier Waves from a source 15 are modulated and transmitted to the transmission line L. At the reproducing terminal, carrier Waves from the line L are impressed upon a demodulator D after amplification in an amplifier 16. The modulating device 14, amplifier 16 and demodulator D may each consist of three electrode electron discharge devices as indicated. A suitable arrangement for synchronously rotating the drums 5 and 6 and modulating and am lifying the carrier waves in accordance with picture currents from the photo-electric cell 11, is disclosed in applicants copending application, Serial'No. 681,347, filed December 18, 1923.

The movable conductors 17 and 18 of a light valve V are connected to the output circuit of demodulator D. The 1i ht valve V controls the amount of light w ich may pass from a source 19 to effect exposure of the light sensitive record blank 10. The light valve V is similar in general arrangement to the light valve disclosed in a copending application of E. C. W ente, Serial No. 635,886, filed May 1, 1923. The movable conductors or strings 17 and 18 are susnded in a magnetic field which is pro- Eficed by a winding 20. A ortion of the strings 17 and 18 are intense y illuminated by hght from source 19 passing through lens 21 and an image of the aperture formed by strings 17 and 18 is projected upon the film 10 by means of the lens 22.

In order that either a positive or a negative of the transparency 9 may be reproduced on the film 10, independently of the received current from line L, a switching circuit is provided in the output circuit of demodulator D. This circuit comprises a series circuit including battery 23, switch 24 and strings 17 and 18, connected across resistance 25. which resistance is connected in series with battery 26. An ammeter 27 is provided to indicate the amount and direction of the current flowing through the light valve.

Battery 23 is of such a value that for a P given li ht condition in the photo-electric cell 11, t e valve V is closed with the switch 24 in one position, andopened with the switch 24 in its other position. For example, assume the dark condition of the photoelectric cell 11 which corresponds to an opaque elemental area of the picture to be transmitted. If the light valve is wide open, the reproduced picture will be a positive of the original; while if the light valve is closed under this condition, the reproduced picture will be a negative of the ori inal.

he positions of the strings 17 and 18 for these two conditions are illustrated in Figs. 4 and 5. In Fig. 4, the strings 17 and 18 are shown fully o ened with respect to an aperture 28 in the ight passage of the light valve. In Fig. 5 the strings are fully closed.

In Fig. 2 there is illustrated a curve showing the relation between the rectified picture current and the current through the light valve. When the current through the light valve has the value 0A, the valve is so adjusted as to be completely open. As the picture current increases in accordance with successively darker elements of the picture, the light valve current also increases in the ositive direction, resulting in a corresponding closure of the valve. Under these conditions a negative reproduction is obtained.

The converse is true when switch 24 is operated to the left, when battery 23 tends to maintain the valve closed and incoming picture currents tend to 0 en the valve, resultin in a positive repro uction.

Iteferrmg now to Fi 3, the modulated carrier waves from the line L are amplified in amplifier 16 and impressed directly upon th'strings 17 and 18 of light valve V by means of transformer 30. The reproducing drum and optical system is the same as in- Fig. 1, like reference characters being used to designate like elements in the two figures.

In order to provide for changing the reproduction from a negative to a positive or vice versa, battery 31 together with switch 24 is connected across a resistance 32, the resistance 32 being connected in series with the strings 17 and 18. The value of the current flowing in strings 17 and 18 due to the potential drop across the resistance 32 is determined by rheostat 33. Changing switch 24 from one operating position to the other, changes the polarity of the potential drop through resistance 32, and hence the direction of the current flow in strings 17 and 18. The value of the direct current component of the current flowing in strings 17 and 18 is adjusted by means of rheostat 33 so that, when no carrier current is superimposed thereon from the amplifier 16, the aperture formed between strings 17 and 18 is either open or closed, depending upon the osition of switch 24. Assume that the dark condition at the photo-electric cell produces carrier current of maximum amplitude, that the valve tends to close when positive potential is impressed upon the string 18 and that the switch 24 is in the position shown to close the valve. The valve will therefore be opened as each negative impulse of maximum carrier current is received and a positive reproduction will result. With the switch 24 thrown in its left hand position, the valve will be closed when the maximum carrier current is received and a negative reproduction will result.

From the foregoing, it is clear that with either of the arrangements of Fig. 1 or Fig. 3, the type ofreproduction such as a negative or a positive may be changed by changing the position of switch 24. The type of reproduction is therefore independent of the current transmitted from the sending terminal and the flexibility of the equipment is greatly increased. It IS obvious that sometimes it may be more desirable to have the reproduction in the form of a negative. At other times a positive may be the preferable form. By the arrangement of this invention, either type may be obtained independently of the sending terminal.

It is not necessary that the picture current from-the photo-electric cell 11 be transmitted as modulations of a carrier wave but it picture currents, an optical arrangement inmay be transmitted directly to the light valve V .with orwithout amplification as the requirements of the circuit demand. The scope of the invention is not to be limited by the specific embodiments shown in the drawing' but only by the appended claims.

What is claimed is:

1. In a system for the transmission of pictures by electricity, means to produce picture currents, means including an electromagnetic light valve for reproducing the picture, and means to change the type *of the reproduced picture from a positive to a negative or vice versa.

2. In a system for the transmission of picture-s by electricity, means to produce picture currents, means including an electro-magnetic light valve for reproducing the picture, and means connected in circuit with said light valve to change the type of the reproduced picture from a positive to a negative or vice versa.

3; In a system for the transmission of pictures by electricity, means to produce picture currents, an optical arrangement including an electro-magnetic light valve for reproducing the picture, a three electrode electron discharge device controlled by said picture currents to o erate said light valve, and means connecte in the output circuit of said discharge device to change the type of the reproduced picture from a positive to a negative or vice versa.

4. In a system for the transmission of pictures by electricity, means to produce cluding an electro-magnetic light valve for reproducing the picture, a three electrodg electron discharge device c ntrolled by sai picture currents to operate said light valve,

a biasing battery connected in series with said light valve, and a reversing switch for interchanging the electrical conditions of the terminals of said light valve whereby the type of the reproduced picture may be changed from a positive to a-negative or V106 versa.

5 In a s stem for the transmission of pic'- tures by electricity, means toproduce picture currents, means to modulate a carrier wave in accordance with said picture ourmodulator, a resistance connected in said rents, a three electrode electron discharge demodulator for demodulating said modulated wave, an output circuit for said deoutput,.circuit an electro-magnetic light valve connecte across said resistance, a batteryconnected in series with said light valve, and a reversing switch connected between said battery and said light valve for reversing the electrical conditions of the terminals of the valve.

6. In a system for the transmission of pictures by electricity, means for producing picture currents, means including a light valve for re roducing a picture, a space discharge device controlled by said currents for operating said valve, and means in the output circuit of said device for changing the type of the reproduced picture from a positive to a negative 'or from a negative to coo crating with said battery to corresponding yvary the open or closed condition of said valve. I 8. In a system for the transmission of pictures by electricity, means for producing picture currents,-an arrangement including a light valve for reproducing the picture as a negative oras a positive, a spacedischarge device controlled by said icture currents to operate said valve, a iasing battery! connected in circuit with said valve adapted to normally maintain said valve 0 en or closed, and a switch cooperating wit said battery to determinethe positive or negative type of the reproduced picture.

9. n a system for. the transmission of pictures by electricity, means for producing, picture currents, means including a light valve for translating said currents into corresponding picture characteristics, a biasing battery adapted to maintain said valve completelyopen when an opaque characteristic of a picture is to be transmitted, means for allowin said battery tomaintain said valve comp etely closed when an opaque characteristic of said picture is to be transmitted, and means controlled by the var ing characteristics of the picture to transmitted for correspondmgly varying the control of said biasing battery over the open or closed condition of said valve.

In witness-whereof, I hereunto subscribe 

